Spinal Cord Inflammation
By far the most common cause of paralysis seen in veterinary medicine involves inflammation of the spinal cord. There are several conditions that fall under this category:
Intervertebral Disc Disease (IVDD)
Sometimes referred to as a ‘slipped disc’, IVDD occurs when a cushioning disc between two vertebrae moves out of place and pushes on the spinal cord, causing pain and inflammation. It happens most commonly in short-legged, long-backed dogs like Dachshunds and Corgis.
In mild cases dogs may show signs like hunched posture and pain. Moderate cases will show weakness in hind limbs and a ‘drunken’ gait, often with knuckling over of the paws (see video: Knuckling in Dogs: How to Test a Dog for Conscious Proprioception). The most severe cases will show full paralysis of affected limbs. If the problem disc is in the neck, all four limbs will be affected. More commonly the disc is in the mid to lower back and so affects only the hindlimbs.
Treatment ranges from rest and pain management to spinal surgery for the more severe cases. Prognosis for return to function varies with the severity of the case, but in most cases is quite good so long as treatment is pursued promptly.
Fibrocartilagenous Embolism (FCE)
This disease presents similarly to IVDD, except rather than disc material pressing on the spinal cord, it is caused by little bits of the disc cartilage obstructing blood flow in the area creating a clot‒ the same principle of what causes a stroke.
Unlike IVDD, this condition usually affects large breed dogs, and often just one side of the body (left or right rather than front or back). While it may be briefly painful (the moment the cartilage shifts), it is non-painful after that. The signs of paresis/paralysis progress quite quickly at first but then stabilize after approximately 12-24 hours.
Treatment involves primarily supportive care and physiotherapy while the body breaks down the clot and restores blood flow to the spinal cord. Most dogs will recover but the process can take time.
Degenerative Myelopathy (DM)
This condition is a slowly progressive disease of the spinal cord that affects older large breed dogs, commonly German Shepherds. The condition first manifests as a lack of coordination in the hind limbs, and progresses to severe weakness followed by paralysis of these legs.
It appears to be caused by a specific genetic mutation that affects the myelin sheath of the spinal cord (specialized fatty cells that protect nerves). At this time there is no known cure for DM. Fortunately, the condition is not painful.
This is a unique condition in dogs where one side of their face appears droopy or flaccid. Dogs with this condition may appear similar to a human who has had a stroke, but fortunately, the underlying cause here isn’t usually so sinister.
Facial paralysis happens when the nerve supplying the muscles of the face (ex. ears, lips, eyelids, nostrils) becomes inflamed. In most cases this is ‘idiopathic’ – there is no discernible reason for the inflammation. Idiopathic facial paralysis sometimes resolves on its own, but is permanent in other cases. Other than having a bit of a silly appearance, these dogs otherwise do just fine.
Less commonly, facial paralysis can be caused by an inner ear infection or a tumor affecting the facial nerve.
Tick paralysis appears as a sudden and rapidly progressive paralysis of the whole body. It is caused by a toxin in the tick’s saliva that attacks the nervous system. Depending on the type of tick, signs may appear 3-10 days after the tick attaches.
Paralysis starts in the hindlimbs and works its way up the body. Within 12-24 hours dogs are unable to walk, and in severe cases, the muscles that control breathing are affected, making the condition life threatening.
For most North American ticks, the prognosis is good provided that the tick is removed promptly and supportive veterinary care is available. Full recovery of muscle strength, however, may take up to a few weeks. Unfortunately, in Australia, there are ticks with more deadly neurotoxins and the prognosis is not as good.
Fractures or Trauma
As in humans, trauma that affects the spinal cord is a well known cause of paralysis. Hit-by-car accidents are the most common culprit in dogs. Another common accident occurs during rough play or dog attacks.
While fairly uncommon, cancer can be a cause of paralysis in dogs, especially in senior pets. Tumours affecting the brain, spinal cord, or individual nerves may be the culprit. Diagnosis is usually made by advanced imaging like CT or MRI and treatment/prognosis will vary depending on type and location of tumor.